Tumor necrosis factor (TNF-α) is a potent cytokine having pro-inflammatory properties that is released by many cell types when stimulated. Studies have shown a relationship between elevated levels of TNF-α and a variety of diseases such as septic shock, hematopoiesis, tumors, and inflammatory disorders of the central nervous system, including HIV encephalitis, cerebral malaria, and meningitis. More recently agents which inhibit the action of TNF-α have demonstrated clinical utility in a variety of diseases such as rheumatoid arthritis, psoriasis, and inflammatory bowel disease. Additionally Certain neurodegenerative diseases such as Alzheimer's disease, Parkinson's disease, and Creutzfeldt-Jacob disease also are reportedly associated with enhanced TNF-α levels. See, e.g., Arvin et al., “The Role of Inflammation and Cytokines in Brain Injury,” Neuroscience and Biobehavioral Reviews, Vol. 20, No. 3 (1996), at pp. 445–452.
Accordingly, various classes of drugs have been researched and developed to inhibit TNF-α production at both transcriptional and translational levels, e.g., corticosteroids, rolipram (a phosphodiesterase IV inhibitor suppressing TNF-α mRNA synthesis), calphostin, and imidazole-type cytokine suppressing anti-inflammatory drugs (CSAIDs). These drugs are useful in treating a variety of diseases. See Dinarello, “Role of Pro- and Anti-Inflammatory Cytokines During Inflammation: Experimental and Clinical Findings, Review, Vol. 0393-974X (1997), at pp. 91–103.
Recently, attention has focussed on the role of Nuclear factor κB (NF-κB) in the activation pathway that leads to production of TNF-α and other inflammatory cytokines and gene products. Besides TNF-α, NF-κB is involved in the regulation of a variety of genes involved in immune function and inflammation. These include the cytokines IL-1, IL-2, IL-6, IL-2Rα, and GM-GSF, the chemokines IL-8, MCP-1 (CCR2), and RANTES, the adhesion molecules, intercellular adhesion molecule-1 (ICAM-1), vascular cellular adhesion molecule-1 (VCAM-1) and E-selectin, the proteases matrix metalloproteinase-1 (MMP-1), MMP-9 and MMP-13, and the pro-inflammatory enzymes cyclooxygenase-2 (COX-2), iNOS, and cPLA2. Thus, inhibition of NF-κB and/or its activation pathway provides a means for treating various diseases including autoimmune diseases, inflammatory diseases, Alzheimer's disease, atherosclerosis, oncogenesis, and so forth by a variety of modes of action (i.e. cytokine reduction, chemokine reduction, reduction of adhesion molecule, decreased expression of certain proteases implicated in inflammatory and immune disease processes, and decreased production of enzymes which produce pro-inflammatory mediators) which have been implicated in a variety of disease progression. See, e.g., Baldwin, “The NF-κB and IκB Proteins: New Discoveries and Insights,” Annual Rev. Immunol., Vol. 14 (1996), at pp. 649–81; see also Christman et al., “Impact of Basic Research on Tomorrow's Medicine, The Role of Nuclear Factor-κB in Pulmonary Diseases,” Chest, Vol. 117 (2000), at pp. 1482–87, and Roshak, et al., “Small-molecule Inhibitors of NF-κB for the Treatment of Inflammatory Joint Disease.” Current Opinion in Pharmacol. Vol. 2 (2002) pp. 316–321.
IκB is a cytoplasmic protein that controls NF-κB activity by retaining NF-κB in the cytoplasm. IκB is phosphorylated by the IκB kinase (IKK), which has two isoforms, IKK-α (“IKK-1”) and IKK-β (“IKK-2”). When IKK phosphorylates IκB, NF-κB is rapidly released from the cytoplasm into the cell. Upon release into the cell, NF-κB translocates to the nucleus where it binds to the promoters of many genes and up-regulates the transcription of pro-inflammatory genes. Thus inhibitors of IKK-1 and/or IKK-2 would prevent translocation of NF-κB to the nucleus and prevent transcription of the pro-inflammatory gene products described above. For example see Burke, et al. “BMS-345541 is a Highly Selective Inhibitor of IκB Kinase that Binds at an Allosteric Site of the Enzyme and Blocks NF-κB dependent Transcription in Mice.” J. Biol. Chem. Vol. 278, (2003) pp. 1450–1456.
The therapeutic effects of glucocorticoids are mediated in part by their ability to inhibit NF-κB activity by two mechanisms, i.e., up-regulating IκB protein levels and inhibiting NF-κB subunits. The deleterious side effects of glucocorticoids (such as osteoporosis, hyperglycemia, fat redistribution, etc.) have been postulated to result from the interaction of glucocorticoids with the glucocorticoid receptor (GR) or the glucocorticoid response element (GRE). For example see Schacke, et al. “Mechanisms Involved in the Side Effects of Glucocorticoids” Pharmacol. and Therapeutics Vol 96 (2002) pp. 23–43. Thus inhibitors of IKK-1 and/or IKK-2 inhibitors should provide much of the therapeutic benefit of glucocorticoids with a greatly improved side effect profile.
As may be appreciated, those in the field of pharmaceutical research continue to seek to develop new compounds and compositions having increased effectiveness, bioavailability, and solubility, having fewer side effects, and/or providing the physician and consumer with a choice of options. Particularly in the area of immune response, many individuals respond differently depending upon the type of treatment and chemical agent used. Mechanisms of action continue to be studied to aid in understanding the immune response and in developing compounds effective for treating inflammatory and immune-related disorders.
The present invention provides triazolopurine-based tricyclic compounds useful as inhibitors of IKK.